Process for manufacturing half-tone phase shifting mask blanks

ABSTRACT

For efficiently manufacturing half-tone phase shifting mask blanks having uniform product qualities, which enables the prevention of optical property variations when the blanks are mass-produced, there is provided a process for manufacturing half-tone phase shifting mask blanks each having a phase shifting film containing at least one half-tone film on a transparent substrate, comprising the step of providing a target containing a metal and silicon, and carrying out reactive sputtering in an atmosphere containing a reactive gas, to form said half-tone film on said transparent substrate, wherein the formation of the half-tone film by said reactive sputtering is carried out using, as said target, a target having a metal/silicon compositional ratio selected so as to give a predetermined optical property of the half-tone film, at a reactive gas flow rate selected from a region where a discharge characteristic is stabilized against a change in the flow rate of the reactive gas.

FIELD OF THE INVENTION

The present invention relates to a process for manufacturing half-tonephase shifting mask blanks, half-tone phase shifting mask blanks andhalf-tone phase shifting masks. More specifically, the present inventionrelates to a process for manufacturing half-tone phase shifting maskblanks, which enables the prevention of optical property variations whenthe blanks are mass-produced, half-tone phase shifting mask blanksobtained by the above process and half-tone phase shifting masksmanufactured from the above mask blanks.

PRIOR ART

In the conventional manufacture of semiconductor devices such as IC andLSI, there has been carried out micro-processing by photolithographyusing a photoresist composition. In the micro-processing, a thin film ofa photoresist composition is formed on a substrate such as a siliconwafer, the photoresist composition is exposed to an actinic ray such asultraviolet ray through a mask having a pattern and then developed toobtain a resist pattern, and the substrate is etched using the resistpattern as a protective film.

In recent years, however, the integration degree of semiconductordevices is rapidly enhanced, and the manufacture of very large scaleintegrated circuits, or the like requires the processing accuracy of anultrafine pattern in a submicron or quarter micron region. Sinceconventional ultraviolet ray used as an exposure light source has alimit imposed by its wavelength, therefore, the wavelength of ray forexposure tends to be decreased, and g-beam, i-beam and far ultravioletbeams such as deep-UV and excimer laser beam have to be used forcarrying out the exposure.

Meanwhile, with regard to DRAM (dynamic random access memory), theframework of their mass production for 256 megabits has been establishedat present, and the integration degree is further being enhanced from amegabit class to a gigabit class. The design rule of integrated circuitsis accordingly being minimized, and it has come to be an immediateproblem to cope with demands for a fine pattern having a line width(half pitch) of 0.10 μm or less.

As one means of coping with the minimizing of a pattern in size, higherresolution of patterns has been so far forward ed by decreasing thewavelength of an exposure light source as described above. As a result,KrF excimer laser beam (248 nm) and ArF excimer laser beam (193 nm) havecome to be mainly used as an exposure light source in currentphotolithography, and further, the application of F₂ excimer laser beam(157 nm) is being studied.

However, on one hand, the above decrease in the wavelength of exposurelight improves the resolution, but on the other hand, the depth of focusdecreases, so that there are caused undesirable events such as anincrease in a burden on the design of optical systems including a lensand a decrease in process stability.

For coping with the above problems, a phase shifting lithography methodhas come to be employed. The phase shifting lithography method is amethod for improving the resolution of photolithography by onlymodifying a mask without modifying an optical system, and in thismethod, exposure beams passing through a photomask are provided with aphase difference, so that the resolution can be remarkably improved onthe basis of an interference between the beams being transmitted. Theabove phase shifting lithography method uses a phase shifting mask as amask for transfer a micro-pattern.

The above phase shifting mask is composed, for example, of a phaseshifter portion forming a pattern portion on a mask and a non-patternportion where no shifter portion is present. The phases of beams passingthrough the above two portions are shifted from each other by 180°, tocause mutual interferences of the beams in the boundary of the pattern,whereby a transferred image is improved in contrast. It is known thatthe phase shifting amount φ (rad) of beam passing through the phaseshifter portion depends upon the real part of complex refractive index(n) of the phase shifter portion and a film thickness (d) and that therelationship of the following expression is established.φ=2πd(n−1)λ  (1)

wherein λ is a wavelength of an exposure beam.

For shifting the phase by 180°, therefore, the film thickness d can bedetermined to be as follows.d=λ/{2(n−1)}  (2)

The above phase shifting mask can attain an increase in the depth offocus for obtaining a necessary resolution, and it can simultaneouslyimprove the resolution and the application of the process withoutchanging the wavelength of exposure beam.

Depending upon light transmissivity of a phase shifter portion forming amask pattern, practically, the phase shifting mask can be largelyclassified into a complete transmission type (Levenson type) phaseshifting mask and a half tone phase shifting mask. The former is a maskin which the light transmissivity of the phase shifter portion isequivalent to the light transmissivity of the non-pattern portion (lighttransmission portion) and which is nearly transparent to the wavelengthof exposure beam. It is generally said to be effective for transferringa line and a space. In the later half-tone type, the lighttransmissivity of the phase shifter portion (light semi-transmissionportion) is several to tens percent of the light transmissivity of thenon-pattern portion (light transmission portion), and it is said to beeffective for making a contact hole and an isolated pattern.

The half-tone phase shifting mask includes a two-layered half-tone phaseshifting mask composed of a layer for mainly adjusting thetransmissivity and a layer for mainly adjusting the phase, and asingle-layered half-tone phase shifting mask that has a simple structureand is easy to manufacture.

At present, the mainstream is a half-tone phase shifting mask whosehalf-tone phase shifter portion is composed of a single layer made of anMoSiN film or MoSiON film.

Generally, the above MoSiN film or MoSiON film is formed by a reactivesputtering method using an MoSi target in a sputtering atmospherecontaining an inert gas and reactive gases such as O₂, N₂, NO₂ and thelike. As an MoSi target, typically, a target having an Mo:Si amountratio of 1:2 (molar ratio) is used. The MoSi-containing film generallytends to show a smaller transmissivity with a decrease in wavelength,and due to a decrease in the wavelength of an exposure beam, there istherefore employed a method in which an MoSi target having a siliconcontent of 70 to 95 mol % is used for obtaining a material film having alarger transmissivity (for example, see Japanese Patent 2989156).Conventionally, the flow rate of a reactive gas is controlled, andoptionally, the composition of a target is controlled, for obtaining afilm having intended optical properties corresponding to the wavelengthof a predetermined exposure beam.

With minimizing LSI patterns, there have been practically used as theexposure light source (wavelength of exposure beam), i-ray (367 nm) andKrF excimer laser beam (248 nm), and recently ArF excimer laser beam(193 nm) have come to be practically used. There are accordinglydemanded half-tone phase shifting masks having phase shifting filmshaving optical properties (transmissivity and phase difference) suitablefor the wavelengths of exposure beams such as i-ray, KrF excimer laserbeam and ArF excimer laser beam. In the mainstream of currentlyavailable half-tone phase shifting masks, films are designed such thattheir half-tone phase shifter portions have an exposure beamtransmissivity of about 6%. However, half-tone phase shifting maskshaving a higher transmissivity are being required for far higherresolutions, and there are increased demands for half-tone phaseshifting mask blanks having various transmissivity properties such as atransmissivity of 9%, 15%, or the like.

In the optical properties of half-tone phase shifting mask blanks,conventionally, it has been required to control the transmissivityvariation to be ±1% and control the phase shifting amount to be ±5°. Inrecent years, however, it has come to be required to attain atransmissivity variation of ±0.4%, desirably, ±0.2% and a phase shiftingamount variation of ±4°, desirably, ±2°. With a decrease in thewavelength of an exposure beam, however, it tends to be still moredifficult to control the above variations to be in the above tolerableranges. When the above various kinds of half-tone phase shifting maskblanks having various optical properties are manufactured with onemass-production apparatus, it has been difficult to set film-formingconditions under which the optical properties do not vary with regard tothe optical properties of each kind.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a process forefficiently manufacturing half-tone phase shifting mask blanks whilepreventing variations of optical properties among the blanks incommercial mass production so that the blanks have uniform qualities;half-tone phase shifting mask blanks manufactured by the above process;and half-tone phase shifting masks manufactured from the above maskblanks.

For achieving the above object, the present inventors have made diligentstudies and as a result found the following. When a half-tone film isformed on a transparent substrate by sputtering a target containing ametal and silicon in an atmosphere containing a reactive gas tomanufacture half-tone phase shifting mask blanks each having a phaseshifting film containing at least one half-tone film on the transparentsubstrate, the above half-tone film is formed under certain conditionsas will be explained later, whereby there can be efficientlymanufactured half-tone phase shifting mask blanks whose optical propertyvariations in mass production are prevented. On the basis of thisfinding, the present invention has been completed.

That is, according to the present invention, there are provided;

(1) a process for manufacturing half-tone phase shifting mask blankseach having a phase shifting film containing at least one half-tone filmon a transparent substrate,

comprising the step of providing a target containing a metal andsilicon, and carrying out reactive sputtering in an atmospherecontaining a reactive gas, to form said half-tone film on saidtransparent substrate,

wherein the formation of the half-tone film by said reactive sputteringis carried out using, as said target, a target having a metal/siliconcompositional ratio selected so as to give a predetermined opticalproperty of the half-tone film, at a reactive gas flow rate selectedfrom a region where a discharge characteristic is stabilized against achange in the flow rate of the reactive gas,

(2) a process for manufacturing a plurality of types of half-tone phaseshifting mask blanks each of which has a phase shifting film containingat least one half-tone film on a transparent substrate, the half-tonefilm of each blank having a different optical property,

comprising the step of providing targets containing a metal and siliconand carrying out reactive sputtering in an atmosphere containing areactive gas, to form said half-tone film on said transparent substrate,

wherein the formation of the half-tone film by said reactive sputteringis carried out using a targets selected from a plurality of targetshaving different metal/silicon compositional ratios so as to givedesired different half-tone film optical properties among the maskblanks, at a reactive gas flow rate selected from a region where adischarge characteristic is stabilized against a change in the reactivegas flow rate,

(3) the process as recited in the above (1) or (2), wherein the reactivegas is at least one member selected from the group consisting ofnitrogen, oxygen, fluorine and compounds of these,

(4) half-tone phase shifting mask blanks manufactured by the processrecited in the above (1), (2) or (3), and

(5) half-tone phase shifting masks manufactured from the half-tone phaseshifting mask blanks recited in the above (4).

The “process for manufacturing phase shifting mask blanks” in the above(1) and (2) should be interpreted in a broad sense, and the process isto include a process for mass-producing phase shifting mask blanks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing an example of a relationship between anitrogen gas flow rate and a discharge voltage when sputtering iscarried out at a constant electric power.

FIG. 2 is a schematic drawing of an example of a DC magnetron sputteringapparatus for manufacturing a half-tone phase shifting mask blanksaccording to a single-substrate system.

FIG. 3 is a schematic drawing of an example of an sputtering apparatusfor manufacturing half-tone phase shifting mask blanks according to anin-line continuous blank manufacturing method.

FIG. 4 is a graph showing variations of phase angles among half-tonephase shifting mask blanks obtained in Example 1.

FIG. 5 is a graph showing variations of transmissivity among half-tonephase shifting mask blanks obtained in Example 1.

FIG. 6 is a graph showing variations of phase angles among half-tonephase shifting mask blanks obtained in Example 2.

FIG. 7 is a graph showing variations of transmissivity among half-tonephase shifting mask blanks obtained in Example 2.

PREFERRED EMBODIMENTS OF THE INVENTION

The process for manufacturing a half-tone phase shifting mask blanks,provided by the present invention, is a process for manufacturinghalf-tone phase shifting mask blanks each having a phase shifting filmcontaining at least one half-tone film on a transparent substrate. Theabove phase shifting film has a single-layered structure or amulti-layered structure of two or more layers. The reactive sputteringis carried out using a target containing a metal and silicon in anatmosphere containing a reactive gas, to form the phase shifting filmcontaining at least one half-tone film.

The phase shifting film having a single-layered structure formed of ahalf-tone film includes, for example, a film composed of a materialcontaining a metal, silicon and at least one member selected from thegroup consisting of oxygen, nitrogen, fluorine, carbon and hydrogen.Examples of the above metal include molybdenum, tantalum, tungsten,chromium, titanium, nickel, palladium, hafnium and zirconium.

The phase shifting film having a multi-layered structure includes, forexample, a phase shifting film formed by stacking two or more of theabove single-layered half-tone films and a phase shifting film formed bystacking the above single-layered half-tone film and atransmissivity-adjustment layer such as a metal layer containing atleast one member selected from the group consisting of chromium,tantalum, hafnium, magnesium, aluminum, titanium, vanadium, yttrium,zirconium, niobium, molybdenum, tin, lanthanum, tungsten and silicon.

For producing a phase shifting effect, the phase shifting film of thepresent invention is set such that the phase difference is approximately180°.

The above reactive gas is at least one member selected from nitrogen,oxygen, carbon, fluorine and compounds of these. Specifically, at leastone of O₂, N₂, NO₂, N₂O, CH₄, CO₂, CF₄ and the like can be used. In thereactive sputtering, a sputtering gas (inert gas) used in combinationwith the above reactive gas includes, for example, Ar, He, Xe andmixtures of these gases.

The material for the above transparent substrate is not critical, andcan be selected from those that are conventionally used as a materialfor a transparent substrate of a half-tone phase shifting mask blanks.Examples of the above material include soda-lime glasses such assoda-lime glass and white crown; low-expansion glasses such asborosilicate glass, alkali-free glass and aluminosilicate glass; quartzglasses such as synthetic quartz and plastic films such as a polyesterfilm. Of these, soda-lime glass and quartz glass are preferred as amaterial for a substrate for masks for LSI and LCD.

In the process of the present invention, the greatest feature is thatthe formation of the half-tone film by reactive sputtering is carriedout using, as the target, a target having a metal/silicon compositionalratio selected so as to give a predetermined optical property of thehalf-tone film, at a reactive gas flow rate selected from a region wherea discharge characteristic is stabilized against a change in the flowrate of the reactive gas. When a plurality of kinds of half-tone phaseshifting mask blanks having half-tone films having different opticalproperties among the mask blanks are mass-produced, there are used atarget selected from a plurality of targets having differentmetal/silicon compositional ratios so as to give predetermined differentoptical properties of the half-tone films among the mask blanks.

The above “region where a discharge characteristic is stabilized” refersto a region where the discharge current or discharge voltage does notshow a substantial change with regard to a change in the flow rate ofthe reactive gas when the sputtering is carried out at a constantvoltage. When the sputtering is carried out at a constant current, itrefers to a region where the discharge electric power or dischargevoltage does not show a substantial change with regard to a change inthe flow rate of the reactive gas. Specifically, it refers to a regionwhere a change in the discharge voltage is within about 20 V when theflow rate of the reactive gas changes by 10 SCCM (standard statecm³/min).

FIG. 1 is a graph showing an example of a relationship between anitrogen gas flow rate and a discharge voltage when sputtering iscarried out at a constant electric power using a target containing amolybdenum and silicon in a molybdenum: silicon molar ratio of 20:80, inwhich the electric power is constantly maintained at 2 kW and argon (Ar:10 SCCM) and nitrogen are used as a sputtering atmosphere. The graphshows a change in discharge voltage relative to a change in the flowrate of nitrogen. As shown in FIG. 1, there are regions where thedischarge voltage shows a small change relative to a change in the flowrate of nitrogen, or the discharge characteristic is stabilized. Thatis, in FIG. 1, there are a stable region where the discharge voltage isapproximately 620 to 630 V at a nitrogen flow rate of approximately 55SCCM or lower and a stable region where the discharge voltage isapproximately 350 V at a nitrogen flow rate of approximately 80 SCCM orgreater.

A change in the discharge characteristic, such as a voltage, has a greatinfluence on the variation of the optical properties, so that thenitrogen flow rate is selected from a region where the discharge voltageis not changed. In FIG. 1, there are two stable regions. In view of theperformances (transmissivity and phase difference) of half-tone films tobe formed, however, it is preferred to set the nitrogen flow rate on thebasis of the later stable region where the discharge voltage isapproximately 350 V.

FIG. 1 shows one embodiment of the sputtering at a constant electricpower where a target containing molybdenum and silicon is used, nitrogenis used as a reactive gas and argon is used as a sputtering gas.However, the above is also applicable to cases where a target having adifferent molybdenum/silicon molar ratio or a target containing othermetal and silicon is used, other reactive gas or other sputtering gas isused, or sputtering is carried out at a constant current.

Then, a plurality of targets having different metal/siliconcompositional ratios are provided, and there is selected a target havinga metal/silicon compositional ratio that gives a predetermined opticalproperty when the gas flow rate determined above is employed. Accordingto experiments made by the present inventors, it has been found that anextinction coefficient of the half-tone film material can be controlledwhen the compositional ratio of the target is finely adjusted, forexample, adjusted at intervals of 0.1 mol % or less.

Therefore, under the gas flow conditions selected from a region wherethe discharge characteristic is stabilized, targets having compositionalratios changed at intervals of 1 mol % or the like are used to formhalf-tone films such that the half-tone films give a predetermined phasedifference (180° in the case of a single layer), and the half-tone filmsare measured for transmissivity. In this manner, the compositional ratioof the target that gives a predetermined transmissivity is determined.

For obtaining a material having high transmissivity, the compositionalratio of the target is preferably selected from compositions having afar larger silicon content than a metal silicide composition having ahigh silicon content among stoichiometrically stable metal silicides.More specifically, the compositional ratio is preferably selected fromcompositions having a silicon content of 70 to 95 mol %. When thesilicon content is less than 70 mol %, it is difficult to obtain amaterial having high transmissivity. For using a beam having a shorterwavelength than that of a KrF excimer laser, the content of silicon ispreferably 78 mol % or more, and for using a beam having a shorterwavelength than that of an ArF excimer laser, the content of silicon ispreferably 85 mol % or more. When the silicon content exceeds 95 mol %,the discharge stability during DC sputtering may be impaired.

As described above, the reactive sputtering is carried out using, as atarget, a target having a metal/silicon compositional ratio selected soas to give a predetermined optical property, at a reactive gas flow rateselected from a region where the discharge characteristic is stabilizedagainst a change in the reactive gas flow rate, whereby there can beformed a half-tone film having a predetermined phase angle andtransmissivity, in which the variations thereof are small, that is, thevariation of the phase angle is generally within ±4°, preferably within±2° and the variation of the transmissivity is generally within ±0.4%,preferably within ±0.2%.

As a method of mass-producing half-tone phase shifting mask blanks inthe present invention, there can be employed any one of asingle-substrate system and an in-line continuous blank manufacturingmethod.

First, the single-substrate system will be explained.

FIG. 2 shows a schematic drawing of an example of a DC magnetronsputtering apparatus for manufacturing half-tone phase shifting maskblanks by a single-substrate system.

The DC magnetron sputtering apparatus has a vacuum chamber 1, and amagnetron cathode 2 and a substrate holder 3 are disposed inside thevacuum chamber 1. A backing plate 4 is attached to the magnetron cathode2, and a sputtering target 5 is attached to the backing plate 4. Thebacking plate 4 is cooled directly or indirectly with a water-coolingsystem (not shown). The magnetron cathode 2, the backing plate 4 and thesputtering target 5 are electrically connected. A transparent substrate6 is attached to the substrate holder 3.

The vacuum chamber 1 is discharged with a vacuum pump through adischarge port 7. After the atmosphere in the vacuum chamber reaches avacuum degree at which the properties of a film to be formed are nolonger affected, a gas mixture containing nitrogen is introduced througha gas introduction port 8, and a negative voltage is applied to themagnetron cathode 2 with a DC power source 9, to carry out sputtering.The pressure inside the vacuum chamber 1 is measured with a pressuregauge 10.

The transparent substrate is introduced into the vacuum chamber 1, andafter a thin film is formed thereon by sputtering in the vacuum chamber1, the thus-manufactured phase shifting mask blank is carried out of theabove vacuum chamber 1. The above series of process is consecutivelycarried out with regard to each of a plurality of transparentsubstrates, and the transparent substrates are introduced at nearlyconstant intervals and the mask blanks are carried out of the vacuumchamber at nearly constant intervals, whereby the time period forforming a film can be made constant among a plurality of mask blanks.

The in-line continuous blank manufacturing method will be explainedbelow. FIG. 3 is a schematic layout of an example of a sputteringapparatus for manufacturing half-tone phase shifting mask blanks by anin-line continuous blank manufacturing method.

In the sputtering apparatus shown in FIG. 3, the formation of films on aplurality of transparent substrates 6 placed on a pallet 11 iscontinuously carried out, and a series of film formations are carriedout while the pallets are transported in one vacuum chamber withchanging supply amounts of reactive gases (O₂, N₂, etc/) in thetransportation direction. In this case, therefore, a multi-layered filmcan be formed in one chamber (having one vacuum degree) by sputtering.Further, a plurality of mask blanks can be simultaneously formed in onechamber. In FIG. 3, reference numeral 12 indicates an introductionchamber, numeral 13 indicates a sputtering chamber, and numeral 14indicates a recovery chamber.

According to the process of the present invention, half-tone phaseshifting mask blanks each having an optical property of which thevariations are controlled and having a uniform product quality can beefficiently manufactured when mass-produced.

According to the present invention, further, there is provided half-tonephase shifting mask blanks manufactured by the above process, and thereis also provided half-tone phase shifting masks manufactured from theabove mask blanks.

The half-tone phase shifting masks of the present invention can bemanufactured by providing mask blanks each having a phase shifting filmcontaining at least one half-tone film formed by the above process, on atransparent substrate, patterning the phase shifting film to remove partthereof according to a predetermined pattern, and thereby forming a maskpattern constituted of a light semi-transmitting portion and a lighttransmitting portion.

The method of the above patterning is not specially limited, and therecan be employed any method which is known in the manufacturing ofconventional half-tone phase shifting masks. For example, an electronbeam resist film is formed on the phase shifting film of a mask blanks,and the resist film is irradiated with electron beam according to apredetermined pattern. Thereafter, the resist is developed to form aresist pattern, and then the phase shifting film is dry-etched withusing the resist pattern as a mask, and the remaining resist pattern ispeeled off (removed), to obtain half-tone phase shifting masks eachhaving a light semi-transmitting portion and a light transmittingportion, provided by the present invention.

EXAMPLES

The present invention will be explained more in detail with reference toExamples hereinafter, while the present invention shall not be limitedby these Examples.

Example 1

A single-layered light semi-transmitting film composed substantially ofmolybdenum, silicon and nitrogen was formed on a transparent substratewith a DC magnetron sputtering apparatus shown in FIG. 2 by a singleblank manufacturing method as described below. In this manner, 250half-tone phase shifting mask blanks for KrF excimer laser beam (248 nm)were manufactured.

As a sputtering target, a target having an Mo:Si molar ratio of20.0:80.0 was used, and as a sputtering gas, a gas mixture containingargon, nitrogen and helium was used (gas flow rate: Ar=10 SCCM, N₂=80SCCM, He=40 SCCM). The light semi-transmitting films were formed suchthat the phase angles of the light semi-transmitting films were adjustedto about 180° in the wavelength of a KrF excimer laser beam. The abovegas flow conditions were selected from a region where the dischargecharacteristic was stabilized.

The blanks were then heat-treated at 250° C. for 30 minutes in aheat-treatment apparatus.

The above phase shifting mask blanks (having a 15.2 cm×15.2 cm squareform) were evaluated for variations of phase angles and transmissivityin the wavelength of the KrF excimer laser beam. In the measurement(evaluation), an average value of data in arbitrary 6 points in ameasurement area having a 13.2 cm×13.2 cm square form was taken as acm×15.2 cm square form) were evaluated for variations of phase anglesand transmissivity in the wavelength of the ArF excimer laser beam inthe same manner as in Example 1. FIGS. 6 and 7 show the results. Thesefigures show that the variation of the phase angle among the blanks waswithin ±1° and that the variation of the transmissivity among the blankswas within ±0.1%. In this Example, there were mass-produced half-tonephase shifting mask blanks each having a stable optical property for ArFexcimer laser beam.

In the above Examples, when a plurality of half-tone phase shifting maskblanks for the wavelengths of different exposure beam are manufactured,the gas condition excellent in discharge stability is fixed, and thecomposition of the target is modified, whereby half-tone phase shiftingmask blanks each having a different optical property can bemass-produced in one and the same apparatus.

Comparative Example 1

For comparison, the same apparatus as that in Example 1 was used, andphase shifting mask blanks were manufactured in the same manner as inExample 1 except that the sputtering gas was replaced with a gas mixturecontaining argon, nitrogen and helium (gas flow rate: Ar=10 SCCM, N₂=60SCCM, He=40 SCCM).

As a result, the variation of the phase angle among the blanks waswithin ±5° and that the variation of the transmissivity among the blankswas within ±1%. That is, value of one substrate measured. FIGS. 4 and 5shows the results. These figures show that the variation of the phaseangle among the blanks was within ±1° and that the variation of thetransmissivity among the blanks was within ±0.1%. In this Example, therewere mass-produced half-tone phase shifting mask blanks having stableoptical properties for KrF excimer laser beam.

Example 2

A single-layered light semi-transmitting film composed substantially ofmolybdenum, silicon and nitrogen was formed on a transparent substratewith the same DC magnetron sputtering apparatus as that used in Example1 by a single blank manufacturing method as described below. In thismanner, 250 half-tone phase shifting mask blanks for ArF excimer laserbeam (193 nm) were manufactured.

As a sputtering target, a target having an Mo:Si molar ratio of10.0:90.0 was used, and as a sputtering gas, a gas mixture containingargon, nitrogen and helium under the same conditions as those in Example1 was used (gas flow rate: Ar=10 SCCM, N₂=80 SCCM, He=40 SCCM). Thelight semi-transmitting films were formed such that the phase angles ofthe light semi-transmitting films were adjusted to about 180° in thewavelength of an ArF excimer laser beam.

Then, the blanks were heat-treated at 250° C. for 30 minutes in aheat-treatment apparatus.

The above phase shifting mask blanks (having a 15.2 the variations weregreater than those in Example 1, and it was hence not possible tomass-produce half-tone phase shifting mask blanks having intended stableoptical properties.

While the above Examples show embodiments of manufacturing two types ofhalf-tone phase shifting mask blanks for the wavelengths of two exposurebeams, half-tone phase shifting mask blanks for the wavelengths of twoor more exposure beams or half-tone phase shifting mask blanks havingdifferent transmissivity values can be naturally mass-produced as well.

The sputtering apparatus shall not be limited to an apparatus accordingto the single blank manufacturing method described in Examples, and itmay be an apparatus according to the in-line continuous blankmanufacturing method.

Further, N₂ used as a reactive gas may be replaced with other reactivegas.

Further, in the above Examples, single-layered half-tone phase shiftingmask blanks were manufactured. However, the present invention can bealso applied to the formation of half-tone phase shifting mask blankseach having a multi-layered structure of two or more layers.

Effect of the Invention

According to the present invention, there can be provided a process formanufacturing half-tone phase shifting mask blanks, which enables theprevention of optical property variations when the blanks aremass-produced, half-tone phase shifting mask blanks obtained by theabove process and half-tone phase shifting masks manufactured from theabove mask blanks.

1. A process for manufacturing half-tone phase shifting mask blanks eachhaving a phase shifting film containing at least one half-tone film on atransparent substrate, comprising the step of providing a targetcontaining a metal and silicon, and carrying out reactive sputtering inan atmosphere containing a reactive gas, to form said half-tone film onsaid transparent substrate, wherein the formation of the half-tone filmby said reactive sputtering is carried out using, as said target, atarget having a metal/silicon compositional ratio selected so as to givea desired phase angle and transmissivity of the half-tone film, at areactive gas flow rate selected from a region where a change in thedischarge voltage is within about 20 V when the flow rate of thereactive gas changes by 10 SCCM (standard state cm³/min).
 2. The processof claim 1, wherein the reactive gas is at least one member selectedfrom the group consisting of nitrogen, oxygen, fluorine and compounds ofthese.
 3. A process for manufacturing a plurality of types of half-tonephase shifting mask blanks each of which has a phase shifting filmcontaining at least one half-tone film on a transparent substrate, thehalf-tone film of each blank having a different optical property,comprising the step of providing targets containing a metal and siliconand carrying out reactive sputtering in an atmosphere containing areactive gas, to form said half-tone film on said transparent substrate,wherein the formation of the half-tone film by said reactive sputteringis carried out using a target selected from a plurality of targetshaving different metal/silicon compositional ratios so as to givedesired different phase angles and transmissivities among the maskblanks, at a reactive gas flow rate selected from a region where achange in the discharge voltage is within about 20 V when the flow rateof the reactive gas changes by 10 SCCM (standard state cm³/min).
 4. Theprocess for manufacturing half-tone phase shifting mask blanks asrecited in claim 1 or 3, wherein the metal/silicon compositional ratioof said target is selected from a region where said target has a siliconcontent of 70 to 95 mol %, to obtain desired optical properties of thehalf-tone film.
 5. The process for manufacturing half-tone phaseshifting mask blanks as recited in claim 1 or 3, wherein themetal/silicon compositional ratio of said target is selected from aregion where said target has a silicon content of 85 to 95 mol %, toobtain desired optical properties of the half-tone film.
 6. The processof claim 3, wherein each of the mask blanks produced has a transmissionvariation of ±0.4%.
 7. The process of claim 3, wherein each of the maskblanks produced has a phase shifting amount variation of ±4°.
 8. Theprocess of claim 1 or 3, wherein the half-tone phase shifting maskblanks are mass-produced.
 9. The process of claim 1 or 3, wherein eachof the mask blanks produced has a transmission variation of no more than1%.
 10. The process of claim 1 or 3, wherein each of the mask blanksproduced has a phase shifting amount variation of no more than ±5°. 11.A method of determining optimum conditions for forming a half-tone filmin the manufacture of a plurality of types of half-tone phase shiftingmask blanks which are for a plurality of wavelengths for exposure orwhich have different transmissivities, by carrying out reactivesputtering in an atmosphere containing a reactive gas using a targetcontaining a metal and silicon, to form a phase shifting film containingat least one half-tone film on a transparent substrate, wherein theformation of the half-tone film by said reactive sputtering is carriedout using, as said target, a plurality of types of targets whosemetal/silicon compositional ratios are selected such that half-tonefilms having desired different phase angles and transmissivities areobtained, at a reactive gas flow rate selected from a region where achange in the discharge voltage is within about 20 V when the flow rateof the reactive gas changes by 10 SCCM (standard state cm³/min).
 12. Themethod of determining optimum conditions for forming a half-tone film asrecited in claim 11, wherein the metal/silicon compositional ratios ofsaid targets are determined in a region where said targets have asilicon content of 70 to 95 mol %, to give desired optical properties ofthe half-tone film.
 13. The method of determining optimum conditions forforming a half-tone film as recited in claim 11, wherein themetal/silicon compositional ratios of said targets are determined in aregion where said targets have a silicon content of 85 to 95 mol %, togive desired optical properties of the half-tone film.
 14. A process formanufacturing half-tone phase shifting mask blanks, which comprisesforming a phase shifting film containing at least one half-tone film ona transparent substrate under conditions determined according to themethod recited in claim
 11. 15. A process for manufacturing half-tonephase shifting masks, which comprises patterning the phase shiftingfilms of the half-tone phase shifting mask blanks manufactured by theprocess recited in claim 14, to form mask patterns.
 16. A process formanufacturing half-tone phase shifting mask blanks each having a phaseshifting film containing at least one half-tone film on a transparentsubstrate, by providing a target containing a metal and silicon andcarrying out reactive sputtering in an atmosphere containing a reactivegas to form said half-tone film on said transparent substrate, theprocess comprising the steps of determining a relationship between areactive gas flow rate and a discharge characteristic of a sputteringapparatus in said reactive sputtering, determining reactive gas flowrate conditions capable of providing mask blanks having a transmissionvariation of ±0.4% and having a phase shifting amount variation of ±4°,on the basis of said relationship between the reactive gas flow rate andthe discharge characteristic, forming half-tone films using targetshaving different metal/silicon compositional ratios under said reactivegas flow rate conditions determined, measuring the half-tone films foran optical property and determining a relationship between thecompositional ratio of the metal and silicone in the target and theoptical property of the half-tone film, determining a target compositionhaving a metal/silicon compositional ratio that gives a predeterminedoptical property, on the basis of said relationship between themetal/silicon compositional ratio and the optical property of thehalf-tone film, and carrying out the reactive sputtering using a targethaving the thus-determined target composition under the thus-determinedreactive gas flow rate conditions, to form the half-tone films on eachtransparent substrate.
 17. A process for manufacturing a plurality oftypes of half-tone phase shifting mask blanks each of which has a phaseshifting film containing at least one half-tone film on a transparentsubstrate, the half-tone film of each blank having a different opticalproperty, by providing targets containing a metal and silicon andcarrying out reactive sputtering in an atmosphere containing a reactivegas to form said half-tone film on said transparent substrate, theprocess comprising the steps of determining a relationship between areactive gas flow rate and a discharge characteristic of a sputteringapparatus in said reactive sputtering, determining reactive gas flowrate conditions capable of providing mask blanks having a transmissionvariation of ±0.4% and having a phase shifting amount variation of ±4°,on the basis of said relationship between the reactive gas flow rate andthe discharge characteristic, forming half-tone films using a pluralityof targets having different metal/silicon compositional ratios undersaid reactive gas flow rate conditions determined, measuring thehalf-tone films for optical properties and determining relationshipsbetween the compositional ratios of the metal and silicone in thetargets and the optical properties of the half-tone films, determiningcompositions of a plurality of different targets having metal/siliconcompositional ratios that give predetermined different opticalproperties, on the basis of said relationships between the metal/siliconcompositional ratios and the optical properties of the half-tone films,and carrying out the reactive sputtering using a plurality of differenttargets having the thus-determined target compositions under thethus-determined reactive gas flow rate conditions, to form the half-tonefilms.
 18. The process of claim 16 or 17, wherein the optical propertyrepresents light transmissivity.
 19. The process of claim 16 or 17,wherein the reactive gas is at least one member selected from the groupconsisting of nitrogen, oxygen, carbon, fluorine and compounds of these.20. The process of claim 19, wherein the reactive gas is nitrogen. 21.The process of claim 16 or 17, wherein the discharge characteristic ofthe sputtering apparatus is a discharge voltage.
 22. The process ofclaim 21, wherein said discharge characteristic stable region is aregion where a change in the discharge voltage is within about 20 V whenthe flow rate of the reactive gas changes by 10 SCCM (standard statecm³/min).
 23. The process of claim 16 or 17, wherein the metal/siliconcompositional ratio is determined in compositions having a siliconcontent of 70 to 95 mol % for obtaining a predetermined transmissivityof said half-tone film.
 24. The process of claim 16 or 17, wherein thehalf-tone phase shifting mask blanks are mass-produced.
 25. A processfor the production of a half-tone phase shifting mask, which comprisespatterning a phase shifting film of a half-tone phase shifting maskblank obtained by the process recited in claim 16 or 17 to form a phaseshifting film pattern on the transparent substrate.